1. Technical Field
This invention generally relates to apparati and methods for analyzing foam, and in particular, to a method and apparatus for analyzing and characterizing fire fighting foam.
2. Background Art
Fire fighting foam has become the method of choice in fighting and extinguishing fires. Foam, for fighting fire, has heretofore been classified very qualitatively, typically by its visual appearance and apparent viscosity. Foam has been divided into five foam types which are: Type 1, refering to a mostly air very dry and fluffy foam; Type 2, refering to a shaving cream consistency which holds peaks and does not immediately run off of a vertical surface; Type 3, refering to a watery shaving cream consistency where the peaks collapse and the foam will not hold on a vertical surface; Type 4, refering to a very wet foam which readily runs off of vertical surfaces; and Type 5, which refers to a mostly water foam which has no body at all. Obviously, this classification system leaves a lot to be desired.
Knowing the foam type is of critical importance, in that different foam types are required depending upon the fuel type of the fire. If a less expensive foam type will adequately extinguish the fire, undue expense can be incurred by using an unnecessarily thick foam.
The three widely accepted techniques for producing fire fighting foam are the water expansion pumping system (WEPS), the compressed air foam system (CAFS), and the free fall foam system (FFFS). Unfortunately, fire fighting foam type, whether produced by the WEPS, the CAFS, or the FFFS, is dependent upon four factors. The first factor is the percent concentration of the foaming agent or surfactant, the second factor is the number of gallons of water per minute expended, the third factor is the cubic feet of air per minute expended, and the fourth factor is the type of equipment, i.e., manifolds, hose dimensions, nozzles, etc. The first three of these factors, i.e. the foaming agent, water and air concentrations, are heavily dependent upon the fourth factor, the equipment type and settings.
Prior to the present invention, foam analysis was accomplished by measuring the foam conductivity or solution drainage rate. A device which measures solution drainage rate is taught by GALES, U.S. Pat. No. 4,084,426. Gales teaches a test tube having a plurality of light emitting diode and phototransistor pairs located at opposing sides of the test tube along its entire length. Digital circuitry successively scans the LED and phototransistor array to determine the point at which the foam and solution interface is located and calculates a drainage/dissipation rate using successive scans. Unfortunately, as will be explained, dissipation rate is not indicative of fire fighting foam type. Hence, the Gales device is unsuitable for classifying fire fighting foam by type.
Recently, there has been a substantial amount of interest in using fire fighting foam on structure fires as well as open range and forest fires. In fighting range and forest fires, water is obviously scarce and in high demand. Accordingly, a fire fighter must determine the foam type necessary to extinguish a particular fire, depending upon the fuel type, considering also the availability of water, number of trips necessary to lay the required foam line, time and progress lost in successive trips and the cost of the foaming agent, e.g. surfactant. In fighting structure fires, on the other hand, scarcity of water is normally not the overriding consideration. Instead the fire fighter must balance the cost of water damage against damages incurred as a result of a slowly extinguished fire.
Typically, water damage far exceeds the actual fire damage. Very few fire stations are equipped with foam generating equipment, simply because highly skilled personnel have heretofore been required to produce the proper foam type for any given fire. In fact, present day foam making is more of an art than a science.
Therefore, what is needed is a fire fighting foam analyzing method and apparatus which requires a minimum amount of skill to accurately characterize foam so that any given piece of foam generating equipment can be calibrated and optimized to produce the necessary foam type.